What is the biggest Catholic Church in Pennsylvania?

"St Patrick's Cathedral in New York City"

***Actually, the Basilica of the National Shrine of the Immaculate Conception in DC is larger than St. Patrick's in NYC. The National Shrine is the largest Roman Catholic church in the U.S., and one of the 10 largest Roman Catholic churches in the world.

you are right person who said the national shrine in dc. but to be more specific about the world part...it is the 7th or 6th largest church in the wolrd i no cuz i went on a field trip to dc and our tour guide said.